Ammit lived near the scales of justice in Duat, the Egyptian underworld. In the Hall of Two Truths, Anubis weighed the heart of a person against the feather of Ma'at, the goddess of truth, which was depicted as an ostrich feather (the feather was often pictured in Ma'at's headdress). If the heart was judged to be not pure, Ammit would devour it, and the person undergoing judgement was not allowed to continue their voyage towards Osiris and immortality. Once Ammit swallowed the heart, the soul was believed to become restless forever; this was called "to die a second time". Ammit was also sometimes said to stand by a lake of fire. In some traditions, the unworthy hearts were cast into the fiery lake to be destroyed. Some scholars believe Ammit and the lake represent the same concept of destruction.

Ammit was not worshipped; instead she embodied all that the Egyptians feared, threatening to bind them to eternal restlessness if they did not follow the principle of Ma'at.

Ammit has been linked[who?] with the goddess Tawaret, who has a similar physical appearance and, as a companion of Bes, also protected others from evil. Other authors[who?] have noted that Ammit's lion characteristics, and the lake of fire, may be pointers to a connection with the goddess Sekhmet. The relation to afterlife punishment and lake of fire location are also shared with the baboon deity Babi.